Berlin 2018 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 49: Terahertz dynamics

MA 49.4: Vortrag

Donnerstag, 15. März 2018, 15:45–16:00, EB 202

Optical generation of femtosecond spin-current pulses in metallic multilayers: optimizing the efficiency — •Alexey Melnikov^1,2, Liane Brandt¹, Mirko Ribow¹, Niklas Liebing¹, Ilya Razdolski², and Georg Woltersdorf¹ — ¹Martin Luther University Halle-Wittenberg, Institute of Physics — ²Fritz Haber Institute of the Max Planck Society, Department of Physical Chemistry

The key challenge in a rapidly emerging field of modern spintronics consists in the push from the GHz to THz domain. In particular, it requires the development of techniques for the generation of femtosecond spin current (SC) pulses. With the help of magneto-induced second harmonic generation (mSHG) in the back pump-front probe scheme, we have demonstrated long-range spin transport on a femtosecond timescale upon laser excitation of the Fe film in epitaxial Fe/Au bi-layers [1]. Later on, in Fe/Au/Fe tri-layers, this technique allowed us to demonstrate 250 fs-short SC pulses and attribute their origin to the non-thermal spin-dependent Seebeck effect at ferromagnet/normal metal interfaces [2]. Here, using both mSHG and magneto-optical Kerr effect detection in similar structures with variable thickness of the Fe emitter, we optimize the excitation of THz standing spin waves [3] and obtain new insights into the underlying electron and spin dynamics. In particular, from the SC generation efficiency dependence on the emitter thickness peaking at 4 nm, we estimate the escape depth of hot majority electrons in Fe of about 2 nm. [1] A. Melnikov et al., PRL 107, 076601 (2011); [2] A. Alekhin et al., PRL 119, 017202 (2017); [3] I. Razdolski et al., Nature Commun. 8, 15007 (2017).